Resistive semiconducting gas sensors are typically cost-efficient and highly sensitive devices. However, due to the detection mechanism based on oxidizing or reducing surface reactions they lack in inherent selectivity. To compensate this, different methods can be applied, as e.g. utilizing catalytic supplements or temperature cycled operation, each with its specific pros and cons. Here we present a new method based on the utilization of surface reaction kinetics by cyclic optical activation in the UV/Vis range. Optical activation enables low temperature operation of the sensing element and therefore reduces the power consumption of the element drastically. This work focuses on the systematic optimization process of the illumination cycle for detection of ozone on nanoporous indium oxide (In2O3) sensing layer.

Thorsten Wagner1, Alexander Weiß2, Sabrina Eichenauer3, Ernst A. Stadlbauer3 Claus-Dieter Kohl2 1 Universität Paderborn, Warburger Straße 100, D-33098 Paderborn, Tel.-Nr.: +49 5251 6

We present a new concept for the detection of hydrogen sulfide (H2S) doses based on percolation effects in semiconducting (p‐type) copper (II) oxide (CuO) thin films. Under H2S exposure at 180 °C CuO undergoes a chemical reaction to metallic conducting copper (II) sulfide (CuS). Reaching a certain dose of H2S (concentration × exposure time) the conductance increases rapidly by two orders of magnitude which is attributed to the formation of CuS percolation paths. This study focuses on the reproducibility of this effect as well as on theoretical modeling of the assumed underlying percolation mechanism. Analysis of conductance data reveals a behavior that is qualitatively very similar to standard scaling theory, but with a lower conductance exponent of µ ≈ 0.85 (instead of 1.3 for 2D systems). The deviation can be explained by a superimposing diffusion process and by deviations of the experimental systems from standard percolation systems. Nevertheless, the CuO thin films exhibit intrinsic structure controlled thresholds for H2S doses, which allows the utilization as H2S dosimeter.Conductance behavior of a CuO thin film exposed to 20 ppm H2S at 180 °C. The percolation threshold pc is reached 1054 s after start of the measurement.

In the course of the climate change and increased focus on CO2-neutral energy sources, the use of wood-driven small heating systems (SHS) becomes more important. But, their contribution to air pollution, especially particulate matter, is about as high as the emissions from car engines. The specific formation of harmful substances in wood fires and possible countermeasures by continuously operating sensor and control systems are covered. Impedance spectra of interdigital electrode (IDE) structures are taken before and after mounting in wood-driven SHS to get information about the particles in the exhaust stream. It appears that the capacitive parts of the impedance spectra at a fixed frequency are appropriate for a fast signal evaluation. The good correlation with established offline measuring methods is discussed and the capability of thermal regeneration is demonstrated. The offline measurements of this work shall give the experimental basis for the development of online measurements in order to control the particle emissions of wood-driven SHS.

Semiconducting copper oxide (CuO) gas sensing layers show a remarkable conductance behavior if exposed to hydrogen sulfide (H2S) gas at low operating temperature (180 degrees C). At first conductance decreases as expected for a p-type semiconducting metal oxide offering reducing test gas. After a certain exposure time, however, a sudden steep increase in conductance can be observed. In a first approach this behavior is explained by the formation of metallic conducting copper sulfide (CuS, degenerate p-type semiconductor) clusters which eventually form conducting pathways across the sensing layers short-circuiting the remaining CuO phase. In the field of statistical physics such behavior can be described by the so-called percolation theory. Here we present a detailed experimental and theoretical analysis of the observed effect utilizing RF-magnetron-sputtered copper oxide films with different stoichiometry (CuO, Cu4O3 and Cu2O) as model systems. The layers are exposed to H2S for different time spans and analyzed with respect to their morphology (SEM, XRD) and chemical composition (XPS, ToF-SIMS). Analysis of the transient behavior of the conductance by means of a percolation model and comparison of the results to the experimental data allow the identification of different processes. For CuO samples first the formation of different non-CuS copper-sulfur-oxygen phases is observed followed by the percolation regime with the steep conductance increase. Afterwards diffusion processes superimposing the percolation leading to a slower conductance increase and eventually the process is dominated by diffusion of copper ions from the bulk. For oxides with other stoichiometry (Cu2O, Cu4O3) no percolation regime is observed which is attributed to higher diffusion rate of copper ions weakening the percolation effect in these samples. Based on these observations a model for the electronic conductance behavior of copper oxide gas sensors under exposure to hydrogen sulfide (H2S) at temperatures below 200 degrees C is proposed. A better understanding of these systems will enable the preparation of reliable sensors with inherent thresholds. (C) 2015 Elsevier B.V. All rights reserved.

MPS-T1-15 # 1 Chemical and Biochemical Sensors Beyond Nernst Response of Sensitivity Enhancement on EIS pH Sensing Device by Multi-Programming. Aurelien Dominguez , YiTing Lin, Chao-Sung Lai* In this study, the effect of different stressing methods on an Electrolyte-Insulator-Semiconductor structure for pH sensing has been studied. The EIS device uses an intermediate trapping storage layer of silicon nitride for the high density of traps of the material. The stressing method consists in using a low field of opposite polarity to the initial stress field to have a relaxation effect on the neutral trap created during the original process [2-3] and to repeat the programming at regular interval of time. With this method we observeD a successful trapping of holes through a negative shift of the flatband voltage and an enhancement of the sensitivity beyond Nernst response, more than THE theoretical ideal case, from 30 mV/pH to 80 mV/pH. In the meantime, by multiple times programming, a great stability with double sensitivity enhancement and variation within ±2% on the sensitivity measurement suggests that this method meets the prerequisite for medical application. 1departement of electrical engineering, GRENOBLE INPPHELMA Grenoble, France 2Department of Electronic Engineering, Chang-Gung University, Taoyuan, Taiwan 3Biosensor Group, Biomedical Engineering Research Center, Chang Gung University, Taoyuan, Taiwan *Phone: +886-3-2118800 ext: 5607 Taiwan

Analysis of infochemicals occurring in low concentrations in the environment increasingly gains in importance. Those information carrier are essential for communication in ecosystems. They facilitate reproduction and, thereby, preservation of species. Volatile signalling substances (pheromones) are efficiently detected by the antennae of insects. By means of electroantennography, the response of the antennae can be read out and analyzed. The viticultural pest European grapevine moth (Lobesia botrana) is controlled by mating disruption, involving the release of synthetic sex pheromones. For further refinement of this method a portable, automated needle trap device connected to a gas chromatograph, mass spectrometer, and electroantennographic detector (NTD-GC-MS/EAD) was developed. The system was successfully applied in the vineyard. As this highly sensitive technique is of limited lifetime, biomimetic approaches based on stable and cost-effective metal-oxide semiconductor gas sensors could be an option. These technologies should be improved in terms of sensitivity by different preparation and measuring techniques. During application in the field, the sensors responded to the pheromone and to other volatile substances in the vineyard. For improvement of the sensor characteristics different temperature regimes and an additional enrichment unit (Needle-Trap-Device, NTD) were tested. A stepwise desorption of the pheromone from the sorbent resulted in mini-mized influence of interfering substances. Coupling of GC-MS/EAD with NTD provides both measurement of very low ambient pheromone concentrations in the vineyard and an assessment of the overall performance of gas sensors for pheromones. Further potential areas of application are i. e. the investigation of the impact of anthropogenic trace compounds on the communication of eusocial insects which are essential pollinators in agro-ecosystems. This means knowledge gained in chemical ecology should be transferred to ecotoxi- ology.

We present a sensor concept based on copper(II)oxide (CuO) nanofibres for the detection of hydrogen peroxide (H2O2) vapour in the percent per volume (% v/v) range. The fibres were produced by using the electrospinning technique. To avoid water condensation in the pores, the fibres were initially modified by an exposure to H2S to get an enclosed surface. By a thermal treatment at 350 degrees C the fibres were oxidised back to CuO. Thereby, the visible pores disappear which was verified by SEM analysis. The fibres show a decrease of resistance with increasing H2O2 concentration which is due to the fact that hydrogen peroxide is an oxidising gas and CuO a p-type semiconductor. The sensor shows a change of resistance within the minute range to the exposure until the maximum concentration of 6.9% v/v H2O2. At operating temperatures below 450 degrees C the corresponding sensor response to a concentration of 4.1% v/v increases. The sensor shows a good reproducibility of the signal at different measurements. CuO seems to be a suitable candidate for the detection of H2O2 vapour at high concentrations. Resistance behaviour of the sensor under exposure to H2O2 vapours between 2.3 and 6.9% v/v at an operating temperature of 450 degrees C.

Pheromones and other semiochemicals play an important role in the natural world by influencing the behavior of plants, mammals, and insects. In the latter case, species-dependent pheromone communication has numerous applications, including the detection, trapping, monitoring and guiding of insects, as well as pest management in agriculture. On-site sensors are desirable when volatile organic compounds (VOCs) are used as semiochemicals. Insects have evolved highly selective sensors for such compounds, so biosensors comprising complete insects, isolated organs or individual proteins can be highly effective. However, isolated insect organs have a limited lifetime as biosensor, so biomimetic approaches are needed for prolonged monitoring, novel applications, or measurements in challenging environments. We discuss the development of on-site biosensors and biomimetic approaches for airborne-pheromone sensing, together with biomimetic VOC sensor systems. Furthermore, the infochemical effect describing the anthropogenic contamination of the ecosystem through semiochemicals, will be considered in the context of novel on-site pheromone sensing-systems.

In this investigation we combined enrichment with different analysis techniques for in situ sensing of the pheromone main component of the European Grapevine Moth (Lobesia botrana). The electroantennographic detection (EAD) offers the lowest in situ detection limit, but has a limited lifetime of only few hours. Based on the enrichment it is possible to pre‐concentrate the natural pheromone level up to a threshold for biomimetic analytic systems. By metal‐oxide semiconductor gas sensors in a ‘selective odorant measurement of a multi‐sensor array’ (SOMMSA) setup it is possible to achieve a system with a suitable lifetime for monitoring applications. Due to the sequential desorption from the enrichment material with increasing temperature steps it is possible to eliminate interfering gas components and therefore increase the selectivity of the complete system and to achieve a tool for monitoring applications, e.g. in a vineyard.

We use Monte-Carlo Simulations to study the conductance switching generated by gas-induced electron trapping/-releasing in films of sintered metal oxide nanoparticles by using a site-bond percolation model. We explore the possibilities of gas sensors based on these mechanisms. In our study, we model films of different thicknesses where the conductance values of the grains (sites) and of the contacts (bonds) between these grains depend on the surface density N-r of adsorbed gas molecules from the ambient atmosphere. Below a critical density N-r = N-r,N-c, the system is insulating due to the interruption of current flow, either through the connecting bonds or through the grain interior. This leads to two competing critical gas covering thresholds N-r,c((bond)) and N-r,c((site)), respectively, that separate the insulating from the conducting phase. For N-r,c((site)) > N-r,c((bond)), the characteristic curve of monodisperse sensors shows a noticeable jump from zero to a finite conductance at N-r = N-r,c((site)), while for polydisperse sensors site percolation effects modify the jump into a steep increase of the characteristic curve and thus lead to an enhanced sensitivity. For N-r,c((site)) < N-r,c((bond)), both mono- and polydisperse systems follow the same curves that show a smoother characteristic increase alpha (N-r - N-r,c((bond)))(2) which reveals that, despite the occurrence of an inherent bond percolation effect close to N-r,N-c, the increase of the bonds is the dominating effect. (C) 2013 AIP Publishing LLC.

The European fire beetle Melanophila cuspidata oviposits on stems damaged by fire to provide its xylophagous larvae with nutrition. We investigated the beetle's ability to estimate the heating stage of the wood beneath the charred bark by means of volatiles. Such biologically preselected volatiles can enable a reliable differentiation between fresh, heated, and burned wood and can be used for early fire warning systems. 25 compounds of heated pine wood chips (Pinus sylvestris) were identified and quantified by GC–MS. Electrophysiological experiments (GC–MS/EAD, EAG) and behavioral studies with M. cuspidata revealed eight electrophysiologically active and behaviorally attractive compounds. Furfural was selected as a marker volatile for heated wood and a nanoporous semiconductor metal oxide gas sensor was developed for the detection of this compound. In a burning chamber, this sensor detected furfural at low concentration prior to the ignition of pine wood chips (P. sylvestris). The furfural emission in this chamber was monitored simultaneously by an online mass-spectrometer. The utilization of M. cuspidata as an information filter for marker volatile selection and the feasibility of the nanoporous sensor for early fire warning systems in the wood processing industry are discussed.

A new type of hydrogen sulfide (H2S) sensor based on a (chemical) phase transformation in copper oxide (CuO; p-type semiconductor) is presented. Layers of electrospun copper oxide fibers show dosimeter-type behavior if exposed to highly diluted H2S at operating temperature of 170 °C. The conductance of these layers remains nearly constant for a certain time period (latency time) after which the conductance increases over several orders of magnitude. The latency time shows a linear dependence on the reciprocal H2S concentration; consequently the layers are acting as dosimeter. The presented sensor shows a switching point at a dose of ca. 210 ppm*s. The effect is reversible; operating the fiber network at 350 °C in air leads to a recovery of the initial conductance; higher doses can therefore be detected by cyclic operation mode. As could be shown the observed behavior is due to the formation of copper sulfide clusters (CuS; degenerate p-type semiconductor) on the outer face of the CuO-fibers. As long as the CuS clusters are disjunct the conductance is not changed effectively. After reaching a critical CuS cluster concentration (percolation threshold) a percolation network is formed. The conductance increases as a function of time and follows a power law for several orders of magnitude, which is in accordance with theoretical model.

The light-enhanced NO2 sensing behavior of mesoporous In2O3 is measured and interpreted by means of a new sensing model. The model aims at explaining (i) the drop in electronic resistance of n-type semiconducting In2O3 under UV light exposure, (ii) the light-enhanced reaction to oxidizing gases, and (iii) the faster reaction and regeneration in mesoporous In2O3 as compared to non-porous material. Contrary to the conventional double Schottky model the dominating factor for the change in resistance is a change of oxygen vacancy donor states (0.18eV below the conduction band) in the bulk phase due to photoreduction, instead of chemisorption. For the faster reaction and regeneration we propose an explanation based on enhanced oxygen diffusion in the In2O3 crystal lattice, specifically dominant in the mesoporous structure. The response of ordered mesoporous In2O3 to NO2 is stronger than in case of unstructured bulk material (with an average grain size of ca. 40nm). The reaction is significantly accelerated by illuminating the samples with UV light. However, the response of the mesoporous material is weaker in the illuminated case.

Tilman Sauerwald, Jörg Hennemann, Claus-Dieter Kohl, Thorsten Wagner, Stefanie Russ 1 Lab of Measurement Technology, University of Saarland, 66123 Saarbrücken, Germany 2 Institute of Applied Physics, Justus Liebig University Giessen, 35392 Giessen, Germany 3 Faculty of Science, Department of Chemistry, University of Paderborn, 33098 Paderborn, Germany 4 Institut für Theoretische Physik, Freie Universität Berlin, 14195 Berlin, Germany

A model is proposed for the drop in electronic resistance of n-type semiconducting indium oxide (In2O3) upon illumination with light (350 nm, 3.5 eV) as well as for the (light-enhanced) sensitivity of In2O3 to oxidizing gases. Essential features of the model are photoreduction and a rate-limiting oxygen-diffusion step. Ordered, mesoporous In2O3 with a high specific surface area serves as a versatile system for experimental studies. Analytical techniques comprise conductivity measurements under a controlled atmosphere (synthetic air, pure N2) and temperature-resolved in-situ Fourier transform infrared (FTIR) spectroscopy. IR measurements reveal that oxygen vacancies form a donor level 0.18 eV below the conduction band.

Results on light-enhanced NO2 sensing utilizing ordered mesoporous In2O3 are presented and interpreted by means of a new sensing model for ordered mesoporous indium oxide (In2O3) [1]. This model aims to explain the drop in electronic resistance of n-type semiconducting In2O3 under UV light exposure as well as the light-enhanced sensing properties to oxidizing gases. Compared to the conventional double Schottky model [2] the dominating factor for the resistance change is a change of oxygen vacancy donor states in the bulk phase due to photoreduction [3]. Comparison of conductivity measurements with varying oxygen partial pressure for ordered mesoporous and non-structured material shows an accumulative behavior in the case of the mesoporous material which can be related to faster photo reduction caused by the nanostructure. IR measurements reveal a donor level of 0.18 eV below the conduction band attributed to oxygen vacancies. The unique properties resulting from the structure allow low-temperature sensing of NO2; especially the recovery times are significantly shorter for the mesoporous material.

We present pheromone measurements of metal-oxide gas sensors in a laboratory setup using a 'selective odorant measurement of a multi-sensor array'. The array was equipped with commercial gas sensors and measured with constant temperatures and a temperature cycle to increase the sensitivity. To compare and to calibrate the measurement of insect pheromones, we used a portable GC-MS with an electro-antennographic detection system for insect antennae. In order to reach a proof of principles for the intended use of the system for in situ analyses in viticulture and the development of a portable biosensor, we tested the sensors with the main component E7, Z9-Dodecadien-1-yl acetate of the pheromone of the grapevine moth (Lobesia botrana). (c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim